<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <script>
        var a = new Promise(function (resolve, reject) {
            setTimeout(function () {
                console.log(1);
                resolve(2);
            })
        });
        a.then(function (param) {//a 只运行了一次
            console.log(param);
        });
        a.then(function (param) {
            console.log(param * 2);
        });


    </script>
</body>
</html>